Almost all electronic devices contain a regulated power supply, which are typically designed to match the requirements of the electronic devices. An important part of these power supplies is a voltage regulator, which functions to maintain their output voltage and/or current within a desired range. A linear regulator is a voltage regulator based on an active device such as a bipolar junction transistor or field effect transistor operating in its “linear region.” A linear regulating device acts substantially like a variable resistor.
A low dropout or LDO regulator is a DC linear voltage regulator which has a very small input-output differential voltage. The regulator dropout voltage determines the lowest usable supply voltage. Due to the increased demand regarding efficiency and the growing problems with the power dissipation in today's systems, low dropout regulators (LDOs) are the preferred choice among linear regulators. Another important characteristic is the quiescent current, or the current flowing through the system when no load is present. Quiescent current causes a difference between the input and output currents. Quiescent current limits the efficiency of the LDO regulators and, thus, should be minimized.
An important part of most voltage regulators is a voltage reference, which provides a reference voltage that is compared against the output of the voltage regulator. Circuitry within the voltage regulator controls the output of the voltage regulator to follow the voltage reference at all times. Therefore, changes of the voltage reference directly and undesirably affect the voltage output of the regulator.